The present invention generally relates to equipment for attenuating noise in gas flow systems, including blowers, compressors, turbines, etc. More particularly, the present invention relates to silencer equipment containing a noise attenuation unit that can be removed and replaced as a unit to maintain the performance of the silencer equipment and, by disposing of the noise attenuation unit at the end of its useful life, protect downstream blowers, compressors, turbines, etc., from damage. The present invention can be applied in conjunction with all methods of attenuating noise caused by inlet or outlet gas streams.
Certain equipment capable of noise/sound attenuation in gas (typically air) flow streams are commonly referred to as silencers in the art. Common sources of undesirable noise levels include, for example, blowers, compressors, turbines, etc., in a variety of installations, including manufacturing plants, bottling plants, laboratories, industrial plants, power generation facilities, waste water treatment plants, etc. Generally, a flowing gas stream through which undesirable noise is propagated from an upstream or downstream source is passed through a flow passage within a silencer, where the noise is attenuated using various means that are generally categorized as absorptive or reactive (also referred to as chambered). Absorptive silencers typically make use of barrier layers, typically steel or other materials known to be effective in interrupting the transmission of sound energy combined with layers of fibrous or cellular (fabric or foam) absorptive material that surrounds the flow passage and attenuates sound by transferring the energy of sound waves to the absorptive material, generally by converting the sound wave energy within the gas to vibrational and/or thermal energy within the absorptive material. Reactive silencers typically make use of pulse chambers connected to the flow passage, annular noise attenuation tubes, or axially-disposed noise attenuation tubes, into which the sound waves are conducted and suppressed. Hybrid silencers also exist that make use of both absorptive and reactive techniques.
Silencers are typically manufactured as dedicated standalone units that are installed inline in a conduit, duct, pipe, or other passage through which the gas stream flows. Examples of conventional silencers include those sold by Universal Silencer of the Fleetguard/Nelson Company, Stoddard Silencer, and Burgess-Manning of Nitram Energy, Inc. Universal Silencer describes silencers in currently existing product instructional materials as “complete weldments or permanently assembled having no replaceable parts.” For air inlet applications, silencers are often used in combination with filters, though again typically as a standalone unit that is often connected between the filter housing and the noise source. However, integrated filter-silencer units are also commercially available, examples of which include the TRIVENT® Series P09 filter silencer manufactured by Endustra Filter Manufacturers, Inc. In a filter-silencer such as the Series P09, the silencer comprises a reactive chamber that forms an integral and permanent part of the filter housing, usually though not necessarily located immediately downstream of the filter element. The filter housing is configured so that the filter element is accessible for removal and replacement, but the components that make up the silencer are not as these components are, as in the aforementioned Universal Silencers, not removable or replaceable. Other commonly available integrated filter-silencers, such as those manufactured by several companies, among them Solberg Manufacturing, include reactive inlet tubes coupled with an absorptive silencer situated downstream or nested within the filter element. This reactive-absorptive filter silencer is again designed to provide access for filter element changes, but the silencer itself is an integral and permanent fixture of the housing, and is not intended to be removed or replaced.
A problem encountered with silencers is the potential damage that can occur downstream as a result of degradation of the silencer components. For example, common dedicated silencers have an exterior primed surface and are designed to handle relatively moisture-free air. However, in virtually all industrial applications, intake air or gas is ambient and therefore only as dry as the relative humidity, and the compression of air and gases creates condensation. The resulting moisture laden air attacks and corrodes the interior surfaces of the silencers. Because silencers are typically downstream of the filter element, the resulting decay of the interior surfaces, as well as the absorptive materials, causes pieces of metal, scale, fabric, foam, etc., to be drawn into the machinery, and can and does cause permanent damage to the equipment. Dedicated reactive-absorptive filter silencers, in which the absorptive silencer unit is permanently located on the inside of or downstream of the filter element, pose the same problem. Even in situations where galvanized steel or stainless steel is employed to inhibit corrosion, these materials do not deter the decay or erosion of the absorptive material or foam, which accumulate moisture, dirt, and oils that have bypassed the filter element or have been transferred during filter changes or neglect. As a result, the absorptive material breaks down and becomes free to enter the equipment inlets, where they can and do cause permanent damage.